Method for producing rubber modified thermoplastic resins

ABSTRACT

Disclosed is a method for producing a rubber modified thermoplastic resin excellent in surface appearance and various properties and high in commercial values which comprises removing an aqueous phase from a two-phase mixture comprises a graft rubber polymer latex (1) obtained by graft polymerization of vinyl monomer on a rubber latex, a thermoplastic resin (2) and an organic agent in an amount of 0.2 to 6 times the weight of all the polymers (3) which is capable of dissolving said thermoplastic resin (2) and has a solubility in water of 5 to 50% by weight at 25° C. and then removing said organic agent and remaining water from the remaining organic phase by a thermal means.

This invention relates to a method for producing a rubber modifiedthermoplastic resin which comprises mixing a graft rubber polymerproduced by graft polymerization of a vinyl monomer on a rubber with athermoplastic resin, and more particularly it relates to a method forvery efficiently producing a rubber modified thermoplastic resinsuperior in dispersibility of graft rubber polymer particles by mixing agraft rubber polymer latex and a thermoplastic resin in the presence ofa specific organic solvent in a high productivity.

Generally, most of the rubber modified thermoplastic resins representedby ABS resins are those obtained by mixing and kneading a polymerobtained by graft polymerization of a vinyl monomer on a rubber latexand a thermoplastic resin. Usually, production of them comprises thesteps of emulsion graft polymerization, coagulation, solidification,dehydration, drying, blending, and melt extrusion. The emulsion graftpolymerization step is a step of producing a graft polymer latex byemulsion graft polymerizing an acrylic monomer, vinyl cyanide monomer,vinyl aromatic monomer, etc. on a diene rubber latex, vinyl rubberlatex, natural rubber latex, silicone rubber latex and the like. Thecoagulation and solidification steps are steps of adding a coagulantsuch as polyvalent salts and acids to the graft polymer latex to destroythe emulsion state and coagulate the polymer and solidifying the polymerinto rigid powders. The dehydration and drying steps are steps ofremoving the aqueous phase from the mixture of the powdered polymer andwater by a means such as centrifugal dehydration or the like and furtherdrying the powders by a means such as flow drying method to obtain drypowders. The blending step is a step of blending said dry powders withother thermoplastic resins and additives such as stabilizer, lubricant,plasticizer, etc. The melt extrusion step is a step of melting, kneadingand extruding the blend materials into strands by screw extruder andpelletizing them.

One of the problems in production and quality of the products broughtabout in the above method of producing rubber modified thermoplasticresins comprising the above steps is firstly that much heat is required.This is because of the use of a large quantity of hot-air at the dryingstep. The second problem is that since the graft rubber polymerparticles are completely coalesced at the coagulating and solidifyingsteps, a large amount of power is required for completely dispersing thecoalescing graft rubber polymer particles in thermoplastic resin at themelting and kneading procedures after the blending step. In the worstcase, it becomes industrially impossible to uniformly disperse the graftrubber polymer particles in the thermoplastic resin.

Some proposals have been made to improve the conventional methods ofproduction of rubber modified thermoplastic resins which have problemsleading to reduction of industrial competitiveness and some of them havebeen industrially practised. One of them has aimed at reduction of heatused at the drying step and has utilized a screw extruder generallycalled a dehydration extruder which has a dehydration function. Theproposed methods of this type are roughly classified into thoseaccording to which the blend of the graft rubber wet powders aftersubjected to coagulation, solidification and dehydration and otherthermoplastic resins and additives or the graft rubber wet powders aloneis fed to said dehydration extruder and those according to which graftrubber polymer latex and coagulant together with other thermoplasticresins and additives, if necessary, are fed to said dehydrationextruder.

According to these methods the reduction of the heat used can beexpected because the drying step at which a large quantity of hot air isused is omitted, but the procedure of dispersing homogeneously the graftrubber polymer particles in the thermoplastic resin is at the same levelas that of the conventional techniques. That is, according to the formermethods as classified, graft rubber polymer particles in completelycoalescing state are treated and thus these methods are the same as theconventional ones from the point of dispersion of particles. Accordingto the latter methods, latex and coagulant firstly mixed in a treatingapparatus and then subjected to dehydration at about 100° C. or lowerand at this time the graft rubber polymer particles are ordinarily inthe coalescing state. Thereafter, with elevation of temperature theparticles melt with the thermoplastic resin and subjected to thekneading procedure. Thus, these methods are different from the formermethods only in the state of the starting materials supplied and aresimilarly the same as the conventional techniques with respect to thedispersion of particles.

There have been further proposed the method where a latex of graftrubber polymer, a coagulant and a monomer are mixed to form a two-phasemixture consisting of an organic phase and an aqueous phase, then theaqueous phase is removed and the monomer contained in the organic phaseis polymerized and another method where the monomer is polymerizedwithout removing the aqueous phase from the two-phase mixture, then theaqueous phase is removed and the polymer is dried. These methods arefree from the stage where the graft rubber polymer particles completelycoalesce with each other and hence are distinguishable from the abovemethod using the dehydration extruder on the dispersion of particles.However, in the former method it is necessary to polymerize the highviscous mixture of graft polymer and monomer without bringing aboutrun-away reaction and thus this method has difficulties in apparatus andoperation and is not necessarily a superior method. Besides, content ofrubber component in rubber modified thermoplastic resins has a greateffect on the basic properties of resins and for this reason it isimpossible to employ the technique by which polymerization isaccomplished at a low conversion of high fluctuation of the conversionas in the usual bulk polymerization and the remaining monomer is removedby devolatizing and the reaction must be proceeded until a highconversion where the fluctuation of the conversion is low is attained.Therefore, the reactants become highly viscous and temperature becomeshigh as compared with even the general bulk polymerization process andso handling of them becomes very difficult. On the other hand, accordingto the latter method, the monomer is polymerized by suspensionpolymerization and viscosity of the reactants is low and heat ofreaction can be easily removed, but dehydration and drying steps arerequired and this method is also not an excellent method like the formermethod.

In order to solve these problems, the inventors have proposed a methodfor producing rubber modified thermoplastic resins using organic agentsand coagulating agents. This method comprises removing in order waterand the organic agents from the mixture of a latex of graft rubberpolymer, a thermoplastic resin, a coagulating agent and an organicagent. The resins produced by this method may contain emulsifier andemulsion polymerization assistants such as emulsifying stabilizer, etc.which come from the latex like the resins produced by the conventionalmethods and these may cause deterioration of colors, thermal stabilityand moldability of the produced resins. Under the circumstances, theinventors have done their best to develop a method in which most of theemulsion polymerization assistant can be removed into aqueous phase andas a result they have found a method for an efficient production ofrubber modified thermoplastic resins excellent in whiteness andtransparency.

As mentioned hereinabove, many proposals have been made for theproduction of rubber modified thermoplastic resins. However, at present,there have not yet been provided the methods according to which both thehomogeneous dispersion of graft rubber polymer particles which isessential for development of the basic properties of the resins and thereduction of heat required are simultaneously attained and the desiredresins of high quality and high competitiveness can be obtained.

This invention provides a method for producing a rubber modifiedthermoplastic resin which makes it possible to attain homogeneousdispersion of graft rubber polymer particles in thermoplastic resin andwhich can achieve a saving of energy.

This invention relates to a method for producing a rubber modifiedthermoplastic resin which comprises removing aqueous phase from atwo-phase mixture comprising a latex of a graft rubber polymer (1)obtained by graft polymerization of a vinyl monomer on a rubber latex, athermoplastic resin (2) and an organic agent in an amount of 0.2 to 6times the weight of all polymers (3) which is capable of dissolving saidthermoplastic resin (2) and has a solubility in water of 5 to 50% byweight at 25° C. and then removing said organic agent and the remainingwater from the remaining organic phase by a thermal means.

According to another embodiment of this invention, the aqueous phase isremoved from said two-phase mixture from which the thermoplastic resin(2) is omitted, then the remaining organic phase is mixed withthermoplastic resin (2) and therafter from the resultant mixture areremoved said organic agent and the remaining water by a thermal means.

According to further another embodiment of this invention, the object ofthis invention can also be achieved by removing aqueous phase from thetwo-phase mixture containing thermoplastic resin (2), then furtheradding thereto thermoplastic resin (4) and removing from the resultingmixture said organic agent and the remaining water by a thermal means

The rubber latex used in this invention includes all of those which havebeen used as the raw materials for rubber modified thermoplastic resins.As examples thereof, mention may be made of latices of diene rubberssuch as polybutadiene, polyisoprene, SBR, etc., those of olefin rubberssuch as ethylenepropylene rubber, ethylene-vinyl acetate rubber, etc.,those of acrylic rubbers such as polyethyl methacrylate, polyethylacrylate, polybutyl methacrylate, polybutyl acrylate, etc., those ofsilicone rubbers such as polydimethylsiloxane, etc. These rubber laticesmay be used singly or in combination of two or more. It is needless tosay that in this invention the kind of rubbers has no limitation and inaddition to those as enumerated above there may be used any latices ofpolymers having a rubber elasticity at the temperatures at which therubber modified thermoplastic resins to be produced are used.

It is very difficult to homogeneously disperse the rubber particlescontained in the rubber latices as mentioned above in thermoplasticresins by the conventional methods and even if it becomes possible,satisfactory properties cannot be developed due to bad compatibilitybetween rubber and thermoplastic resin. Therefore, graft polymerizationis employed as a means to improve the compatibility and to make possiblethe dispersion of rubber particles thereby to develop excellentproperties.

Vinyl monomers are used for this graft polymerization because thepolymerization method is emulsion radical polymerization and it iscommon to choose the optimum vinyl monomer considering the compatibilityand adhesion with the thermoplastic resin to be blended. The same thingcan also be applied to this invention. Thus, the vinyl monomers used inthis invention for graft polymerization on rubbers include those whichhave been hitherto used, namely, vinyl, cyanide monomers such asacrylonitrile, methacrylonitrile etc., vinyl aromatic monomers such asstyrene, α-methyl styrene, etc., methacrylates such as methylmethacrylate, phenyl methacrylate, etc., halogenated vinyl monomers suchas methyl chloroacrylate, 2-chloroethyl methacrylate, etc., and otherradical polymerizable monomers.

The thermoplastic resins (2) used in this invention include all of thosewhich are soluble in the organic agents mentioned hereinafter and thetypical examples thereof are acrylonitrile-styrene copolymers,acrylonitrile-α- methylstyrene copolymers,acrylonitrile-α-methylstyrene-N-phenylmaleimide copolymers,polystyrenes, polymethyl methacrylate, polyvinyl chloride,polycarbonate, polysulfone, polyethylene terephthalate and the like.

As thermoplastic resins (4), mention may be made of those which satisfythe same conditions as for the thermoplastic resins (2) and examplesthereof are the same as those of thermoplastic resins (2).

Thermoplastic resins (2) and (4) used may be the same or different.

Whether the thermoplastic resin (2) is mixed before or after the removalof aqueous phase from the two-phase mixture may be determined dependingon the affinity between the graft rubber polymer or the thermoplasticresin and the organic agent used. When the affinity between the graftrubber polymer and the organic agent is too great, if thermoplasticresin (2) is added after aqueous phase has been removed from thetwo-phase mixture free of thermoplastic resin (2), it sometimes occursthat dissolving and mixing effects of the organic agent are insufficientand thermoplastic resin (2) is not fully mixed to result in insufficientdispersion of the graft rubber polymer particles in the thermoplasticresin. In this case, desirably, the organic agent is added to thetwo-phase mixture before the aqueous phase is removed therefrom and whenthe graft rubber polymer and the thermoplastic resin coexist.

On the other hand, since the volumetric proportion of the aqueous phasein the two-phase mixture is usually the same as or more than that of theorganic phase, addition of thermoplastic resin (2) after the aqueousphase has been removed from the two-phase mixture has the advantage ofincrease of volumetric efficiency of apparatuses employed because theaqueous phase and the thermoplastic resin do not coexist.

The organic agents used in this invention are those which have asolubility in water of 5 to 50% by weight at 25° C., namely, which iscontained in an amount of 5 g to 50 g in 100 g of aqueous solution at25° C. and which can dissolve said thermoplastic resins (2) and (4).This organic agent can be used in an amount of 0.2-6 times, preferably0.2-2 times the weight of all polymers including thermoplastic resins(2) and (4).

As examples of the organic agents which satisfy the above conditions,mention may be made of single agents such as methyl ethyl ketone, methylacetate, ethyl acetate, diethyl cellosolve, ethyl cellosolve acetate,furfural, trioxan, methyl formate, ethyl formate, propylene oxide,2-pentanol, 2-butanol, isobutanol, n-butanol, acrylonitrile and thelike, mixed agents of two or more of these agents and mixed agentsobtained by mixing an organic agent having a solubility in water at 25°C. of 5% by weight or more such as acetone, methanol, ethanol,n-propanol, isopropanol, formic acid, acetic acid, propionic acid,dioxane, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide,N,N-dimethylsulfoxide, ethyl cellosolve, phenol or the like with anorganic agent having a solubility in water at 25° C. of 5% by weight orless such as toluene, xylene, benzene, chloroform, methylene chloride,dimethyl ether, isopropyl ether, tetrachloroethane, ethylbenzene,styrene, methyl methacrylate or the like in such a manner that theorganic agents are contained in an amount of within the range of 5 to50% by weight in the aqueous phase formed in this invention. For examplewhen 60 parts by weight of water, 15 parts by weight of ispropyl etherand 25 parts by weight of ethanol were mixed, the mixture separates intoan aqueous phase composed of 86% by weight of water, 11% by weight ofisopropyl ether and 3% by weight of ethanol and an organic phasecontaining some water. In this case, it is interpretted in thisinvention that the solubility of the mixed agent composed of 15 parts ofisopropyl ether and 25 parts of ethanol in 60 parts of water is 14% byweight.

In this invention it is necessary to use such organic agent within therange of 0.2 to 6 times the weight of all polymers. When less than 0.2time, the effects of this invention cannot be developed and when morethan 6 times, a big heat energy is required for recovery of the agentsand thus industrial merits are reduced.

According to this invention, when graft rubber polymer latex (1),thermoplastic resin (2) (which may be absent at this stage) and theorganic agent as explained hereinabove are mixed, the mixture separatesinto an organic phase composed of graft rubber polymer, thermoplasticresin (2) (if present), the organic agent, a slight amount or smallamount of a polymerization assistant soluble in said organic agent, etc.and an aqueous phase composed of the organic agent, water and most ofthe polymerization assistant, etc. The aqueous phase is firstlyseparated from this two-phase mixture by common means such asdecantation, centrifugal dehydration, press-dehydration, etc. When theorganic phase is heated to remove the organic agent and a slight amountof remaining water by the conventional devolatizing method, there can beobtained a rubber modified thermoplastic resin having graft rubberpolymer particles homogeneously dispersed in the thermoplastic resin andcontaining substantially no emulsion polymerization assistant.

The reason why the graft rubber polymer particles can be homogeneouslydispersed in the thermoplastic resin according to this invention isconsidered that the graft rubber polymer particles are always in thedispersed or softly agglomerated state through the course of productionuntil a final product without the conventional step at which the graftrubber polymer particles completely adhere to each other. The reason whythe emulsion polymerization assistants such as emulsifier mostly migrateinto the aqueous phase side is considered that a suitable amount of theorganic agent is dissolved in the aqueous phase and the dissolving powerof the aqueous phase for the emulsion polymerization assistantincreases. Furthermore, this invention does not require use of dryerswhich has caused a large quantity of heat loss and makes possible theproduction by the common devices having devolatizing function such asvented extruders, film type evaporators, etc. Thus, this invention makesa great contribution on production cost to the rubber modifiedthermoplastic resin industries.

The following examples and reference examples illustrate the method ofthis invention and effects attained by this invention. The parts inthese examples and reference examples are all by weight.

EXAMPLE 1

Acrylonitrile and styrene were graft polymerized on polybutadiene latexof 0.36 μm in average particle diameter in accordance with theformulation of Table 1 to obtain a latex of graft rubber polymer.

                  TABLE 1                                                         ______________________________________                                        Polybutadiene latex   114.3  parts                                            (Polybutadiene        40     parts)                                           Acrylonitrile         15     parts                                            Styrene               45     parts                                            Sodium laurate        0.5    part                                             Sodium hydroxide      0.01   part                                             Rongalite             0.2    part                                             Ferrous sulfate       0.002  part                                             EDTA-di-sodium salt   0.1    part                                             Tertiary butyl hydroperoxide                                                                        0.3    part                                             Laurylmercaptan       0.3    part                                             Deionized water       125    parts                                            Polymerization temperature                                                                          70°                                                                           C.                                               Polymerization time   240    minutes                                          ______________________________________                                    

An acrylonitrile-styrene copolymer as a thermoplastic resin was preparedin accordance with the formulation of Table 2.

                  TABLE 2                                                         ______________________________________                                        Acrylonitrile          25     parts                                           Styrene                75     parts                                           Azobisisobutyronitrile 0.3    part                                            Laurylmercaptan        0.5    part                                            POVAL (polymerization degree 900)                                                                    0.07   part                                            Sodium sulfate         0.3    part                                            Water                  250    parts                                           Polymerization temperature                                                                           75°                                                                           C.                                              Polymerization time    240    minutes                                         ______________________________________                                    

After completion of polymerization, the resultant suspension ofacrylonitrile-styrene copolymer was subjected to centrifugal dehydrationand dried at 80° C. to obtain a powder of said copolymer.

Then, 300 parts of said latex of graft rubber polymer, 150 parts ofmethyl ethyl ketone, 0.3 part of Irganox 1076 (trademark for agingresister of Ciba-Geigy Co.) and one part of Armide HT (trademark formolding assistant of Lion Armour Co.) were mixed to obtain a mixedliquid which separated into an aqueous phase and a high viscous organicphase. The organic phase was treated by a twin-screw extruder to removeremaining aqueous phase and the polymer was molded into pellets by avented extruder while devolatizing and releasing methyl ethyl ketonecontained in the organic phase. The thus obtained pellets had smoothsurface and non-homogeneous portions, called "fish eye", were not found.These pellets were injection molded at 230° C. to make various testpieces and various properties were measured to obtain the results asshown in Table 3. These results show that the rubber modifiedthermoplastic resin produced in this Example is excellent.

                                      TABLE 3                                     __________________________________________________________________________    Items      Test Methods*    Results                                           __________________________________________________________________________    Tensile yield strength                                                                   ASTM D-638 (20° C.)                                                                     475                                                                              Kg/cm.sup.2                                    Izod impact strength                                                                     ASTM D-256 (20° C. 1/4" notched)                                                        31 Kg cm/cm                                                  (0° C. 1/4" notched)                                                                    25 Kg cm/cm                                       Rockwell hardness                                                                        ASTM D-785 (R scale)                                                                           109                                               Melt flow rate                                                                           ASTM D-1238 (200° C., 5 Kg)                                                             2.3                                                                              g/10 min                                       Yellowness index                                                                         ASTM D-1925      15                                                __________________________________________________________________________     *Same in the following Examples and Reference Examples.                  

EXAMPLE 2

A latex of graft rubber polymer was prepared using the same agents as inExample 1 in accordance with the formulation of Table 4.

                  TABLE 4                                                         ______________________________________                                        Polybutadiene latex   228.6  parts                                            (Polybutadiene        80     parts)                                           Acrylonitrile         5      parts                                            Styrene               15     parts                                            Sodium laurate        0.4    part                                             Sodium hydroxide      0.01   part                                             Rongalite             0.15   part                                             Ferrous sulfate       0.001  part                                             EDTA-di-sodium salt   0.05   part                                             Tertiary-butyl peroxide                                                                             0.1    part                                             Laurylmercaptan       0.1    part                                             Deionized water       50     parts                                            Polymerization temperature                                                                          70°                                                                           C.                                               Polymerization time   280    minutes                                          ______________________________________                                    

When 50 parts of thus obtained graft rubber polymer latex, 85 parts ofthe acrylonitrile-styrene copolymer as used in Example 1 and 80 parts ofa mixed agent composed of 80% by weight of toluene and by weight ofisopropanol were mixed, the resulting mixed liquid separated into twophases as in Example 1 and 0.1 part of Irganox 1076 and 0.5 part ofArmide HT were added thereto. The organic phase was treated and moldedinto pellets in the same manner as in Example 1. The surface of thepellets was smooth and no fish eye was recognized. These pellets wereinjection molded at 230° C. to produce various test pieces and variousproperties thereof were measured in the same manner as in Example 1 toobtain the results as shown in Table 5. These results show that therubber modified thermoplastic resin made in this Example is excellent.

                  TABLE 5                                                         ______________________________________                                        Items             Results                                                     ______________________________________                                        Tensile yield strength                                                                          460       Kg/cm.sup.2                                       Izod impact strength                                                                            (20° C.) 29                                                                      Kg cm/cm                                          "                 (0° C.) 26                                                                       Kg cm/cm                                          Rockwell hardness 111                                                         Melt flow rate    2.3       g/10 min                                          Yellowness index  8                                                           ______________________________________                                    

EXAMPLE 3

Methyl methacrylate and methyl acrylate were graft polymerized on SBRrubber latex of 0.14 μm in average particle diameter in accordance withthe formulation of Table 6 to obtain a latex of graft rubber polymer.

                  TABLE 6                                                         ______________________________________                                        SBR rubber latex      100    parts                                            (SBR rubber           50     parts)                                           Methyl methacrylate   45     parts                                            Methyl acrylate       5      parts                                            Potassium rosinate    1      part                                             Rongalite             0.2    part                                             Ferrous sulfate       0.003  part                                             EDTA-di-sodium salt   0.1    part                                             Cumene hydroperoxide  0.4    part                                             Octylmercaptan        0.2    part                                             Deionized water       150    parts                                            Polymerization temperature                                                                          65°                                                                           C.                                               Polymerization time   240    minutes                                          ______________________________________                                    

Polymethyl methacrylate as a thermoplastic resin was produced inaccordance with the formulation of Table 7.

                  TABLE 7                                                         ______________________________________                                        Methyl methacrylate    100    parts                                           Azobisisobutyronitrile 0.3    part                                            Laurylmercaptan        0.5    part                                            Poval (polymerization degree 900)                                                                    0.07   part                                            Sodium sulfate         0.25   part                                            Water                  200    parts                                           Polymerization temperature                                                                           80°                                                                           C.                                              Polymerization time    180    minutes                                         ______________________________________                                    

After completion of polymerization, the obtained suspension ofpolymethyl methacrylate was subjected to centrifugal dehydration anddried at 80° C. to obtain a powder of the polymer.

When 90 parts of said latex of graft rubber polymer, 70 parts of saidpolymethyl methacrylate powder, 100 parts of ethyl acetate were mixed,the resulting mixed liquid separated into an aqueous phase and a highviscous organic phase. Removal of the aqueous phase, devolatization ofethyl acetate and pelletization were carried out by the apparatus usedin the Example 1. The surface of thus obtained pellets was smooth and nofish eye was recognized. These pellets were injection molded at 220° C.to make various test pieces and various properties were measured toobtain the results as shown in Table 8. These results indicate that therubber modified thermoplastic resin is excellent.

                  TABLE 8                                                         ______________________________________                                        Item           Test methods Results                                           ______________________________________                                        Total light transmission                                                                     ASTM D-1003  89%                                               Dynstat impact strength                                                                      DIN 53453    16 Kg cm/cm.sup.2                                 Rockwell hardness                                                                            ASTM D-785   77                                                               (M scale)                                                      ______________________________________                                    

REFERENCE EXAMPLE 1

The latex of graft rubber polymer produced in Example 1 was coagulatedwith sulfuric acid by a conventional method and the obtained polymer wetpowder was subjected to washing, dehydration and drying to obtain graftrubber polymer dry powder. This graft rubber polymer, theacrylonitrile-styrene copolymer produced in Example 1 and a slightamount of the additives used in Example 1 were mixed and formed intopellets by a screw extruder. The composition of these pellets was thesame as that of the pellets obtained in Example 1, but there were manyfish eyes on the surface. Thus, the pellets obtained in this ReferenceExample had no value as commercial products. Furthermore, these pelletswere injection molded and subjected to the same tests as in Example 1 toobtain the results as shown in Table 9.

                  TABLE 9                                                         ______________________________________                                        Item              Results                                                     ______________________________________                                        Tensile yield strength                                                                          475       Kg/cm.sup.2                                       Izod impact strength                                                                            (20° C.) 21                                                                      Kg cm/cm                                          "                 (0° C.) 16                                                                       Kg cm/cm                                          Rockwell hardness 109                                                         Melt flow rate    2.0       g/10 min                                          ______________________________________                                    

EXAMPLE 4

When 300 parts of the same graft rubber polymer latex as in Example 1,400 parts of methyl ethyl ketone, 0.3 part of Irganox 1076 (trademarkfor aging resister of Ciba-Geigy Co.) and one part of Armide HT(trademark for molding assistant of Lion Armour Co.) were mixed, theresulting mixed liquid separated into an aqueous phase and a highviscous organic phase. This was treated by a twin-screw extruder toseparate the aqueous phase from the organic phase. To the organic phasewas added 150 parts of the acrylonitrile-styrene copolymer as used inExample 1. This was formed into pellets by a vented extruder whiledevolatizing methyl ethyl ketone contained in the high viscous organicphase. Thus obtained pellets had a smooth surface and there were nonon-homogeneous portions called fish eye. These pellets were injectionmolded at 230° C. to make various test pieces and properties thereofwere measured to obtain the results as shown in Table 10. These resultsindicate that the rubber modified thermoplastic resin produced in thisexample is excellent.

                                      TABLE 10                                    __________________________________________________________________________    Items      Test methods     Results                                           __________________________________________________________________________    Tensile yield strength                                                                   ASTM D-638 (20° C.)                                                                     490                                                                              Kg/cm.sup.2                                    Izod impact strength                                                                     ASTM D-256 (20° C., 1/4" notched)                                                       30 Kg cm/cm                                                  ASTM D-256 (0° C., 1/4" notched)                                                        24 Kg cm/cm                                       Rockwell hardness                                                                        ASTM D-785 (R scale)                                                                           110                                               Melt flow rate                                                                           ASTM D-1238 (200° C., 5 Kg)                                                             2.2                                                                              g/10 min                                       Yellowness index                                                                         ASTM D-1925      15                                                __________________________________________________________________________

EXAMPLE 5

50 parts of the same graft rubber polymer latex as used in Example 2 and100 parts of a mixed solvent composed of 80% by weight of ethyl benzeneand 20% by weight of ethanol were mixed to obtain a mixed liquid whichseparated into two phases as in Example 1. This was dehydrated bypressing and to the resulting organic phase were added 85 parts of thesame thermoplastic resin (acrylonitrile-styrene copolymer) as used inExample 1, 0.1 part of Irganox 1076 and 0.5 part of Armide HT. Thisorganic phase was formed into pellets by a vented extruder whiledevolatizing ethylbenzene and ethanol. Thus obtained pellets had asmooth surface and no fish eyes were recognized. The pellets wereinjection molded to make various test pieces and properties thereof weremeasured in the same manner as in Example 1 to obtain the results asgiven in Table 11. These results indicate that the rubber modifiedthermoplastic resin produced in this Example is excellent.

                  TABLE 11                                                        ______________________________________                                        Items                Results                                                  ______________________________________                                        Tensile yield strength                                                                             460    Kg/cm.sup.2                                       Izod Impact strength (20° C.)                                                               33     Kg cm/cm                                          Izod Impact strength (0° C.)                                                                27     Kg cm/cm                                          Rockwell hardness    108                                                      Melt flow rate       2.0    g/10 min                                          Yellowness index     7                                                        ______________________________________                                    

EXAMPLE 6

60 parts of the same graft rubber polymer latex as used in Example 3 and100 parts of ethyl acetate were mixed to obtain a mixed liquid whichseparated into an aqueous phase and a high viscous organic phase. Thismixed liquid was dehydrated by the same apparatus as used in Example 1and to thus obtained organic phase was added 80 parts of the samepolymethyl methacrylate as used in Example 3, followed by devolatizing apart of ethyl acetate by a film type evaporator. Thereafter, the polymerwas formed into pellets by a vented extruder while devolatizing theremaining ethyl acetate. These pellets had a smooth surface and no fisheye was seen. These pellets were injection molded at 220° C. to maketest pieces and properties thereof were measured to obtain the resultsas shown in Table 12. These results show that the rubber modifiedthermoplastic resin produced in this Example is excellent.

                  TABLE 12                                                        ______________________________________                                        Items          Test methods Results                                           ______________________________________                                        Total light transmission                                                                     ASTM D-1003  92%                                               Dynstat impact strength                                                                      DIN 53453    13 Kg cm/cm.sup.2                                 Rockwell hardness                                                                            ASTM D-785   86                                                               (M scale)                                                      ______________________________________                                    

EXAMPLES 7

300 parts of the same graft rubber polymer latex as used in Example 1,50 parts of the same copolymer as used in Example 1, 40 parts of methylethyl ketone and the same assistant as used in Example 1 were mixed toobtain a mixed liquid which separated into an aqueous phase and a highviscous organic phase. After removal of water, 100 parts of saidcopolymer was further added thereto. The organic phase was taken out andpassed through two press rolls to remove superfluous aqueous phase,followed by adding said molding assistant in the same amount as above.Thereafter, the polymer was shaped into pellets by a vented extruderwhile devolatizing methyl ethyl ketone contained in the high viscousorganic phase. Thus obtained pellets had a smooth surface and there wereno fish eyes. They were injection molded at 230° C. to make test piecesand properties thereof were measured to obtain the results as given inTable 13. These results show that the rubber modified thermoplasticresin is excellent one.

                                      TABLE 13                                    __________________________________________________________________________    Items      Test methods     Results                                           __________________________________________________________________________    Tensile yield strength                                                                   ASTM D-638 (20° C.)                                                                     480                                                                              Kg/cm.sup.2                                    Izod impact strength                                                                     ASTM D-256 (20° C., 1/4" notched)                                                       32 Kg cm/cm                                                  (0° C., 1/4" notched)                                                                   24 Kg cm/cm                                       Rockwell hardness                                                                        ASTM D-785 (R scale)                                                                           110                                               Melt flow rate                                                                           ASTM D-1238 (200° C., 5 Kg)                                                             2.2                                                                              g/10 min                                       Yellowness index                                                                         ASTM D-1925      14                                                __________________________________________________________________________

EXAMPLE 8

50 parts of the same graft rubber polymer latex as used in Example 2, 10parts of the same acrylonitrile-styrene copolymer as used in Example 1and 15 parts of a mixed agent consisting of 80% by weight of toluene and20% by weight of isopropanol were mixed to obtain a mixed liquid whichseparated into two phases as in Example 1. The aqueous phase was removedtherefrom and 75 parts of said copolymer was further added to theorganic phase and then 0.1 part of Irganox 1076 and 0.5 part of ArmideHT were added thereto. This was treated and formed into pellets in thesame manner as in Example 1. The surface of thus obtained pellets wassmooth and no fish eyes were present. These pellets were injectionmolded at 230° C. to make test pieces and some properties thereof weremeasured to obtain the results as shown in Table 14. It is recognizedfrom these results that the rubber modified thermoplastic resin obtainedin this Example is superior.

                  TABLE 14                                                        ______________________________________                                        Items             Results                                                     ______________________________________                                        Tensile yield strength                                                                          470       kg/cm.sup.2                                       Izod impact strength                                                                            (20° C.) 30                                                                      Kg cm/cm                                          "                 (0° C.) 25                                                                       Kg cm/cm                                          Rockwell hardness 110                                                         Melt flow rate    2.1       g/10 min                                          Yellowness index  9                                                           ______________________________________                                    

EXAMPLE 9

90 parts of the same graft rubber polymer latex as used in Example 3, 20parts of the same polymethyl methacrylate powder as used in Example 3and 15 parts of ethyl acetate were mixed to obtain a mixed liquid whichseparated into two phases as in Example 1 and 50 parts of saidpolymethyl methacrylate powder was further added thereto. Removal ofaqueous phase, devolatization of ethyl acetate and pelletization werecarried out by the same apparatus as used in Example 1. These pelletshad a smooth surface and no fishing eyes were present. The pellets wereinjection molded at 220° C. to make test pieces and properties thereofwere measured in the same manner as in Example 1 to obtain the resultsas given in Table 15. These results show the excellence of the rubbermodified thermoplastic resin produced in this Example.

                  TABLE 15                                                        ______________________________________                                        Items          Test methods Results                                           ______________________________________                                        Total light transmission                                                                     ASTM D-1003  93%                                               Dynstat impact strength                                                                      DIN 53453    15 Kg cm/cm.sup.2                                 Rockwell hardness                                                                            ASTM D-785   76                                                               (M scale)                                                      ______________________________________                                    

As explained above, according to the method of this invention it becomeseasy to uniformly disperse graft rubber polymer particles in athermoplastic resin and besides it becomes possible to produce resinsexcellent in whiteness and transparency. Furthermore, it becomespossible to convert a graft rubber polymer into a rubber modifiedthermoplastic resin without drying the graft rubber polymer with a largequantity of hot air. This means that rubber modified thermoplasticresins excellent in surface appearance and various properties and highin commercial value can be produced at low costs.

What is claimed is:
 1. A method for producing a rubber modifiedthermoplastic resin which comprises removing an aqueous phase from atwo-phase mixture comprising a graft rubber polymer latex (1) obtainedby graft polymerization of vinyl monomer on a rubber latex, athermoplastic resin (2) which is soluble in an organic agent, and theorganic agent in an amount of 0.2 to 6 times the weight of all thepolymers (3) which is capable of dissolving said thermoplastic resin (2)and has a solubility in water of 5 to 50% by weight at 25° C., whereinthe said organic agent comprises methyl ethyl ketone, methyl acetate,ethyl acetate, diethyl cellosolve, ethyl cellosolve acetate, furfural,trioxan, methyl formate, ethyl formate, propylene oxide, 2-pentanol,2-butanol, isobutanol, n-butanol, acrylonitrile, or a mixed agentcomprising a first agent and a second agent, wherein the first agentcomprises acetone, methanol, ethanol, n-propanol, iso-propanol, formicacid, acetic acid, propionic acid, dioxane, tetrahydrofuran,N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylsulfoxide,ethyl cellosolve, or phenol, and wherein the second agent comprisestoluene, xylene, benzene, chloroform, methylene chloride, dimethylether, isopropyl ether, tetrachloroethane, ethylbenzene, styrene, ormethyl methacrylate; and then removing said organic agent and remainingwater from the remaining organic phase by a thermal means.
 2. A methodfor producing a rubber modified thermoplastic resin according to claim 1which comprises removing the aqueous phase from the two-phase mixturefrom which the thermoplastic resin (2) is omitted, then adding thethermoplastic resin (2) to the remaining organic phase and thereafterremoving from the resulting mixture the organic agent and the remainingwater by a thermal means.
 3. A method for producing a rubber modifiedthermoplastic resin according to claim 1 which comprises removing theaqueous phase from the two-phase mixture, then further adding athermoplastic resin (4) thereto and removing from the resultant mixturethe organic agent and the remaining water by a thermal means.
 4. Themethod of claim 1, comprising using as the said rubber latexpolybutadiene, polyisoprene, SBR, ethylenepropylene rubber,ethylene-vinyl acetate rubber, polyethyl methacrylate, polyethylacrylate, polybutyl methacrylate, polybutyl acrylate, orpolydimethylsiloxane.
 5. The method of claim 1, comprising using as thesaid vinyl monomer acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, methyl methacrylate, phenyl methacrylate, methyl chloracrylate,or 2-chlorethyl methacrylate.
 6. The method of claim 1, comprising usingthe said organic agent in an amount of 0.2 to 2 times the weight of allpolymers.
 7. The method of claim 1, wherein the thermoplastic resin (2)comprises an acrylonitrile-styrene copolymer, anacrylonitrile-α-methylstyrene copolymer, anacrylonitrile-α-methylstyrene-N-phenylm:aleimide copolymer, apolystyrene, a polymethyl methacrylate, a polyvinyl chloride, apolycarbonate, a polysulfone, or a polyethylene terephthalate.